Core Java - Interview Questions and Answers for 'Core java' | Search Interview Question

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Q1051. What data type Variable can be used in a switch statement ?

Core Java

Ans. Variables used in a switch statement can only be a byte, short, int, or char ( and String with Java 7 and above )

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Q1052. What are the sub classes of Exception class?

Core Java

Ans. The Exception class has two main subclasses : IOException class and RuntimeException Class.

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Q1053. How finally used under Exception Handling?

Core Java

Ans. The finally keyword is used to create a block of code that follows a try block. A finally block of code always executes, whether or not an exception has occurred.

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Q1054. What things should be kept in mind while creating your own exceptions in Java?

Core Java

Ans. All exceptions must be a child of Throwable.

If you want to write a checked exception that is automatically enforced by the Handle or Declare Rule, you need to extend the Exception class.

You want to write a runtime exception, you need to extend the RuntimeException class.

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Q1055. What is Comparable Interface?

Core Java

Ans. It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered.

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Q1056. Explain Set Interface?

Core Java

Ans. It is a collection of element which cannot contain duplicate elements. The Set interface contains only methods inherited from Collection and adds the restriction that duplicate elements are prohibited.

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Q1057. What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?

Core Java

Ans. The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented

Sample Code for InputStream

Sample Code for OutputStream

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Q1058. Which Java operator is right associative?

Core Java

Ans. The = operator is right associative.

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Q1059. What is the difference between a break statement and a continue statement?

Core Java

Ans. Break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.

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Q1060. What is the purpose of the System class?

Core Java

Ans. The purpose of the System class is to provide access to system resources.

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Q1061. Variable of the boolean type is automatically initialized as?

Core Java

Ans. The default value of the boolean type is false.

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Q1062. Can try statements be nested?

Core Java

Ans. Yes

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Q1063. What is Externalizable interface?

Core Java

Ans. Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism.

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Q1064. What is the difference between the size and capacity of a Vector?

Core Java

Ans. The size is the number of elements actually stored in the vector, while capacity is the maximum number of elements it can store at a given instance of time.

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Q1065. What is an enumeration?

Core Java

Ans. An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration is obtained. It allows sequential access to all the elements stored in the collection.

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Q1066. What is constructor chaining and how is it achieved in Java?

Core Java

Ans. A child object constructor always first needs to construct its parent. In Java it is done via an implicit call to the no-args constructor as the first statement

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Q1067. Why Java provides default constructor ?

Core Java

Ans. At the beginning of an object's life, the Java virtual machine (JVM) allocates memory on the heap to accommodate the object's instance variables. When that memory is first allocated, however, the data it contains is unpredictable. If the memory were used as is, the behavior of the object would also be unpredictable. To guard against such a scenario, Java makes certain that memory is initialized, at least to predictable default values before it is used by any code.

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Q1068. In a case where there are no instance variables what does the default constructor initialize?

Core Java

Ans. Java expects the superclass ( Object Class ) constructor to be called while creation of any object. So super constructor is called in case there are no instance variables to initialize.

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Q1069. What are the features of encapsulation ?

Core Java

Ans. Combine the data of our application and its manipulation at one place.

Encapsulation Allow the state of an object to be accessed and modified through behaviors.

Reduce the coupling of modules and increase the cohesion inside them.

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Q1070. What are different ways to create String Object? Explain.

Core Java

Ans. There are total six ways

1. literals

When we create a String using double quotes, JVM looks in the String pool to find if any other String is stored with same value. If found, it just returns the reference to that String object else it creates a new String object with given value and stores it in the String pool.

2. new keyword

When we use new operator, JVM creates the String object but dont store it into the String Pool. We can use intern() method to store the String object into String pool or return the reference if there is already a String with equal value present in the pool.

3. string buffer
4. string builder
5. System.out.println
6. char to string

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Q1071. Write a method to check if input String is Palindrome?

Core Java

Ans. private static boolean isPalindrome(String str) {

if (str == null)
return false;

StringBuilder strBuilder = new StringBuilder(str);

strBuilder.reverse();

return strBuilder.toString().equals(str);

}

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Q1072. Write a method that will remove given character from the String?

Core Java

Ans.

private static String removeChar(String str, char c) {    

   if (str == null)        

      return null;     

   

   return str.replaceAll(Character.toString(c), "");

}

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Q1073. Which String class methods are used to make string upper case or lower case?

Core Java

Ans. toUpperCase and toLowerCase

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Q1074. How to convert String to byte array and vice versa?

Core Java

Ans. We can use String getBytes() method to convert String to byte array and we can use String constructor new String(byte[] arr) to convert byte array to String.

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Asked multiple times in Capgemini.

Q1075. Why Char array is preferred over String for storing password?

Core Java

Ans. String is immutable in java and stored in String pool. Once it's created it stays in the pool until unless garbage collected, so even though we are done with password it's available in memory for longer duration and there is no way to avoid it. It's a security risk because anyone having access to memory dump can find the password as clear text.

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Q1076. Why String is popular HashMap key in Java?

Core Java

Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys.

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Q1077. public class a {
   public static void main(String args[]){
      final String s1=""job"";
      final String s2=""seeker"";
      String s3=s1.concat(s2);
      String s4=""jobseeker"";
      System.out.println(s3==s4); // Output 1
      System.out.println(s3.hashCode()==s4.hashCode()); Output 2
   }
}

What will be the Output 1 and Output 2 ?

Core Java

Ans. S3 and S4 are pointing to different memory location and hence Output 1 will be false.

Hash code is generated to be used as hash key in some of the collections in Java and is calculated using string characters and its length. As they both are same string literals, and hence their hashcode is same.Output 2 will be true.

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Q1078. What is the use of HashCode in objects ?

Core Java

Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc.

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Frequently asked to fresh graduates and less experienced.

Q1079. Difference between Composition and Inheritance ?

Core Java

Ans. Inheritance means a object inheriting reusable properties of the base class. Compositions means that an abject holds other objects.

In Inheritance there is only one object in memory ( derived object ) whereas in Composition , parent object holds references of all composed objects.

From Design perspective - Inheritance is "is a" relationship among objects whereas Composition is "has a" relationship among objects.

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Q1080. Will finally be called always if all code has been kept in try block ?

Core Java

Ans. The only time finally won't be called is if you call System.exit() or if the JVM crashes first.

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